The Science of Trail Shoes: How to Pick a Trail Shoe

Martyn Shorten

As noted in the first part of this series, trail shoes are as individual as the runners using them and the conditions trail racers face.  Part II of the series deals to some tips on how to pick a trail shoe based on the  research of Martyn Shorten, PhD, a shoe scientist and head of Biomechanica LLC, a Portland, Oregon company that helps design and test athletic shoes.

"I'd divide them into three classes," says Shorten of the trail shoes.  The first is the "urban trail shoe," which is for mostly runners "running on groomed trails,"  and/or want a trail shoe to run through the snow in the winter.  "A regular shoe will do most of the job, most of the time," says Shorten.  A shoe similar to the one they would normally wear for running on the roads or wet grass.  Many of the shoe companies make trail versions of their road shoes.  The difference being that the trail versions will have a more rugged outsole, a little more traction, water proofing, toe bumper, and a sturdy upper.

These shoes use treatment, material, and/or construction strategies to manage moisture.  For example, a GoreTex upper or treatment with ion masking to keep water out, perhaps gussets to drain water.  "Water always goes in," Shorten notes, and the trail adapted shoe has a way to let it get out.  Though, he notes, water is going to get in, so the best strategy of water management is often a good pair of socks that doesn't retain that water and, in cold conditions keeps your feet relatively dry and warm.

The second category of trail shoes are what Shorten calls "Off Road trail shoes."  These are designed for ungroomed terrain that is uneven, often has sections with rocks and/or forest debris, tree roots, etc.  These are "real trail shoes," rather than adapted road shoes.  More rugged, more luggy(more studs on the bottom to help with traction on soft, muddy, and or loose surfaces).  They have more abrasion resistant mesh on the upper.  They have a "full sole," not one with an arch cut out, for a more stable base so that side to side motion is minimized.

Pronation control is not the major issue for trail runners, Shortyn adds, it's helping to minimize the risk of "rolling," spraining your ankle.  "Total ground contact , a bigger base of support" helps achieve this.  These trail shoes will also have a "plate" in the sole to protect your feet from rocks or other hard, sharp hazards from bruising the bottom of the feet.  And a lacing system with big eyelets, often molded to allow for a smoother movement of the laces as your foot copes with the uneven surfaces, even when the shoe gets wet and/or muddy.

Finally, there is the "Hard Core Mountain Shoe" for extreme terrain.  As these are primarily worn for racing on the mountain running circuit, the shoes should be a "lightweight, flexible, low to the ground package," says Shorten.  Tighter weave in mesh uppers, a rock plate made of lightweight thermoplastic, more rubber on the toe area and possibly around side of shoe as well.  These shoes can weigh as light as from 12 to 8 ounces, yet provide all the toughness necessary for navigating the often sharp, rocky trails.

They have a more abrasion-resistant mesh and a tough rubber outsole.  Some of these specialty shoes may also have "posts" in the midsole to control pronation, the cushioning(usually molded rubber) is firmer, and there is a "substantial structure" around the foot, helping keep the foot stable along with the flat base of the sole.

The flexibility of the shoe is largely a matter of preference, Shorten says.  Usually the top racers want a more flexible shoe as flexibility is more of an issue for speed.  The faster you run, the more flexibility is preferred, but Shorten notes, the great majority of trail runners are not moving at high speed, they may average nine or ten minute mile pace, so flexibility is not a big issue. "Having super flexibility isn't an issue," he says.

"If it feels comfortable," says Shorten, that is more important than flexibility.  Part of that comfort is a non chafing upper.  "So many of the shoes have seamless construction," says Shorten.  Peal Izumi created the first seam-free uppers and now most of the companies produce seam free constructed uppers where the only sewing may be for the tongue of the shoe.  This freedom from ridges and seams helps minimize friction and the potential for blisters.

Running biomechanics is pretty much the same for trail and road running, says Shorten, so the decision on what shoe to wear comes down to the variables of course location, course condition, racing speed, and personal preference.  There is no magic formula or "one size fits all" for trail shoes.  Like running training it can be more "trial and error," figuring out what works for you.